Apparatus in a powder sprayer

ABSTRACT

A powder sprayer for the powder coating of an object is provided with an annular charging channel (9) for electrostatic charging of the powder. The channel is defined by an inner, longitudinal rod (8) and an outer tube, (7), both being manufactured of electrically insulating material. The rod (8) is centered in the tube (7) by means of spacer and turbulence members (10) with vanes which are obliquely inclined or helically configurated in relation to the longitudinal direction of the sprayer. In order to improve the charging and blending of the powder, the turbulators (10) are arranged pair-wise after one another, each with a plurality of vanes which are distributed about the rod (8) so that through flow channels are formed between the vanes. The vanes in adjacent turbulators (10) are, in this instance, offset in the circumferential direction in relation to one another, so that the leading edges of the vanes in a downstream turbulator (10) lie in register with the through flow channels in an upstream turbulator (10).

TECHNICAL FIELD

The present invention relates to an apparatus in a powder sprayer whichcomprises an annular, friction charging channel defined by an innerlongitudinal body and an outer tubular body surrounding the inner body,there being disposed, in the flow path of the powder through thesprayer, at least one turbulator with turbulence members which areobliquely inclined or are helically configurated in relation to thelongitudinal direction of the sprayer.

BACKGROUND ART

In such powder sprayers--or sprayguns--as are employed for painting andlacquering work, and as utilise electrostatic charging of the powder,attempts have been made, with a view to increasing the charging degreeof the powder, to realise as good a turbulence and blending of theair-powder mixture as possible in the charging channel or channelsemployed in the powder spraygun. One method of achieving this has beento make the configuration of the channel proper irregular, spiral or ofdiffering cross-section, so that turbulence will thereby be created.Examples of such constructions are disclosed in Swedish PatentApplications Nos. 7206316-7 and 8007919-7.

Another prior art method of increasing the turbulence and improving thecharging degree in a powder spraygun with friction charging entails thata helicoid rotational movement is imparted to the powder at the sametime as the powder runs through the charging channel in the gun. Oneexample of such a construction is described in U.S. Pat. Ser. No.4,359,192.

In summing up the prior art technology, it might be said that, givenfavourable conditions, it may very well be enough to provide sufficientcharging of the powder. However, if the powder is not of a uniform orhomogeneous nature, but consists of mixtures of different powdervarieties or qualities, the prior art constructions do not functionsatisfactorily. In addition, problems have arisen in certain cases, inthat the powder has received an uneven charge, such that certainparticles in the powder flow have been greatly charged while others havebeen but moderately charged or not charged at all.

OBJECTS OF THE INVENTION

The present invention has for its object to realise an apparatus of thetype disclosed by way of introduction, the apparatus being designed insuch a manner that it generally improves the charging degree of thesprayed powder, even if the powder is not of a unitary nature, and alsounder otherwise unfavourable conditions. Hence, the present inventionhas for its object to design the apparatus disclosed by way ofintroduction in such a manner that sufficient turbulence is created inthe powder flow, as this runs through a friction charging channel. Theinvention further has for its object to realise a more even charging ofthe powder and to attain such a design of the spraygun that the gun maybe manufactured both simply and cheaply, that parts exposed to wear mayreadily be replaced and that the gun may easily be cleaned.

SOLUTION

The objects forming the basis of the present invention will be achievedif the apparatus disclosed by way of introduction is characterised inthat at least two turbulators are disposed in the annular channel andthat turbulence members in proximally located turbulators are offset inthe circumferential direction in relation to one another.

In one preferred embodiment of the apparatus according to the presentinvention, the turbulators are disposed in groups of two or more inmutual sequence after one another.

According to the present invention, the turbulence members are suitablyalso in the form of vanes projecting out from the inner body, the outerportions of the vanes abutting against the inside of the tubular body,each turbulator including a plurality of vanes uniformly distributedabout the inner body such that through flow channels are formed betweenthe vanes.

As a result of these constructional features, there will be ensured anaccurate centering of the inner body in the outer body such that,thereby, the annular charging channel will have the intendedconfiguration and size. Furthermore, the advantage will be gainedaccording to the present invention that the turbulators may simply bemanufactured in the same manner as for spirally cut gear wheels.

A further appropriate feature according to the present invention is thatthe cross-sectional area of a vane is less than the through flow area ina channel.

Moreover, it should also apply according to the present invention thatthe annular channel is of greater radial extent along those portionswhere the turbulators are located than along other portions of theannular channel.

Yet further advantages will be attained if the subject matter of thepresent invention is also given one or more of the characterisingfeatures as set forth in appended claims 6-8.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The nature of the present invention and its aspects will be more readilyunderstood from the following brief description of the accompanyingDrawings, and discussion relating thereto.

In the accompanying Drawings:

FIG. 1 is a longitudinal, approximately diametric cross-section throughthe subject matter of the present invention;

FIG. 2 is a part magnification of the area ringed A in FIG 1;

FIG. 3 schematically illustrates, on a larger scale, two mutuallysubsquent turbulence members according to the invention; and

FIG. 4 is a section taken along the line B--B in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the Drawings, FIG. 1 shows a schematic longitudinalcross-section through the powder spraygun, the right-hand end thereofbeing intended for mounting of a spray nozzle which, as evenly aspossible, distributes a powder-air mixture passing through the powderspraygun for charging of the powder.

In the left-hand end of the Figure, the powder spraygun has an inletdevice 1 with an inlet nipple 2 for connection to a hose conduit throughwhich a fluidised mixture of powder and air is passed. There is furtherprovided an air inlet 3 for the regulated supply of extra air, this airbeing led, through a channel system, into an annular space 4 in order toflow out therefrom via an annular gap 5 and be mixed with the major flowof air and powder which is emitted centrally via the channel 6.

The powder spraygun proper consists of an outer tubular body or a tube 7of electrically insulating material, preferably Teflon ®. Possibly, thetubular body 7 may also consist of another, for example electricallyconductive material and be coated interiorly with a layer ofelectrically insulating material, for example Teflon ® or other suitableplastics material. Interiorly in the outer body or tube 7, there isdisposed an inner rod-shaped body 8 or core which also consists of anelectrically insulating material, preferably of the same material as theelectrically insulating material of the outer body or tube. The innercore 8 is of slightly smaller outer diameter than the inner diameter ofthe outer body or tube, so that there is formed, between these twoparts, a friction charging channel 9 in the form of an annular channel.The inner core 8 is centred in the tube 7 in that the inner core isprovided with a number of centering members 10 which also serve asturbulators. The centering members or turbulators 10 are, therefore,shaped as screws with large pitch or as gear wheels with helically cutcogs, such that there is formed a number of channels which are helicallyconfigurated or are obliquely inclined in relation to the longitudinaldirection of the gun, these channels placing the different sections ofthe charging channel in communication with one another. As a result, thecentering members or turbulators 10 will impart rotary movement to thepowder-air mixture which flows in the charging channel, so that the flowpattern will be turbulent and vortical, whereby the powder particleswill come into improved contact with the channel walls.

A more detailed description of the turbulators 10 will be given below.

An inner conductor 11 of metal such as brass, copper, silver or the likeis embedded or otherwise disposed interiorly in the inner body 8 orcore, the conductor 11 being in the form of a longitudinal rod extendingthroughout substantially the entire length of the inner body 8. The endof the inner conductor facing the inlet device 1 is spiculated to a tipand is there in electric contact with contact springs 12 which arepreferably manufactured of metal. The contact springs 12 are anchored inand extend through the outer tube 7 and are, on the outside thereof, inelectric communication with a hood 13 which is manufactured of metal andsurrounds the inlet device 1 and a portion of the outer tube 7. The hood13 and the inner conductor 11 will hereby be in electric contact withone another.

On the outside of the outer tube 7, there is disposed an outer electricconductor 14 whose detailed construction is more readily apparent fromFIG. 2. The outer conductor 14 is electrically well-connected to thehood 13, is tubular and extends along substantially the entire outersurface of the tube 7. Hereby, the outer conductor 14 will surround theannular charging channel 9 substantially throughout its entire length.Correspondingly, the annular charging channel will surround the innerconductor 11, also throughout substantially the entire length of theannular charging channel.

FIG. 2 shows a large-scale magnification of the ringed portion of FIG. 1marked A. It will be apparent from FIG. 2 that the hood 13 connects tothe outer tube 7 as closely as is practically feasible. Furthermore,there is disposed on the outer surface of the tube 7 a layer 15 of apulverulent electric conductor such as graphite, metal particles, carbonparticles or the like. Outside the conductive pulverulent layer 15,there is disposed a metal foil, metal tube, metal mesh or some similarpowerfully electrically conductive material which may be of a relativelyweak material, so that it is readily deformable but neverthelesssufficiently robust to provide a good electric conductive capacity. Inthe illustrated embodiment, use is made of a metal foil which hasreference numeral 16 and connects to the outside of the hood 13. On theoutside of the metal foil 16, there is provided a shrink-on hose ofplastics material which is shrunk on about the metal foil, the hood 13and the pulverulent conductive layer 15. As a result of the relativelylarge shrink-on force of the shrink-on hose 17, an extremely intimatecontact will be established between the pulverulent layer 15 and theouter tube 7, which, in the Figure, is intimated in that the pulverulentlayer 15 is partly shown as embedded in the outer peripheral surface ofthe tube 7. In the same manner, there will be established, as a resultof the effect of the shrink-on hose, good electric contact between thepulverulent layer 15 and the superjacent metal foil 16. Naturally, goodelectric contact will also be ensured between the metal foil 16 and thehood 13.

As was intimated above, the outer tube 7 need not be a thick-walled tubeof plastics material. Instead, the outer tube may be a metal tube whichis provided with an interior lining of the relevant plastics material.Hereby, the pulverulent layer 15 and the metal foil 16 could bedispensed with, if the outer metal tube is electrically connected to thehood 13 or its counterpart, and, in addition, to the inner conductor 11.

While not being apparent from the Drawing, the hood 13 is suitablyprovided with an electric connection terminal so that the inner andouter conductors may have the same potential and, moreover, a potentialwhich is linked to earth or to the object which is to be sprayed.

As was briefly mentioned above, the purpose of the turbulators 10 ispartly to realise the favourable turbulence in the powder-air mixture asit passes through the charging channel 9, and partly to centre the innerbody or core 8 with the inner conductor 11. For practical reasons, theouter tube or body 7 should be interiorly cylindrical, whereby allturbulators 10 may be of the same dimensions.

For manufacturing reasons, the inner core 8 is suitably divided into anumber of sections in mutual sequence and produced as separated parts.These parts are then joined together in that they are provided with acentral bore for accommodating the inner conductor 11 which, in itsturn, holds together the whole of the inner core 8 by means of a threadconnection or other suitable provision.

According to the present invention, the turbulators are arranged ingroups of two and two, or more, in mutual sequence. A plurality of suchgroups may be disposed along the inner body or core 8 and, in onepractical embodiment, three groups each of two turbulators have provedsuitable. The first group of turbulators 10 (most proximal the inletdevice 1) is disposed immediately adjacent an inlet cone 18 to thecharging channel 9. This inlet cone 18 may, in a practical design, beprovided with an inner thread which cooperates with a mating thread onthe inner conductor 11 so that, thereby, the inlet cone 18 may functionas a nut which unites the whole of the inner body or core 8.

At its major end, the the inlet cone 18 is of slightly smaller diameterthan the major portion of the inner body or core 8, so that, thereby,the charging channel 9 will have a slightly larger radial extentimmediately ahead of the first turbulator 10. Correspondingly, thecharging channel is of slightly greater radial depth immediately afterthe turbulators. This feature is achieved in that the parts 19, inaddition to the turbulators 10 and the inlet cone 18, of which the innercore 8 is composed, are provided with conical or tapering portions 20whose smallest diameter approximately corresponds to the diameter of themajor end of the inlet cone 18.

Each turbulator 10 includes a number of turbulence members 21 which arein the form of vanes projecting out from the inner core 8 and areuniformly distributed about the inner core so that there are formed,between adjacent vanes, through flow channels 23 which guide the powderflow into a vortical flow pattern. The radially outer portions of thevanes are formed to follow the contour of the inner surface of thetubular body 7, and the longitudinal direction of the vanes is obliquelyinclined, or makes an angle with, the longitudinal direction of thecharging channel 9. Furthermore, the vanes 21 may be eitherapproximately straight or arched such that the pitch of the vanes willeither be constant throughout the entire length, or increase or decreasealong this length.

In order that the flow resistance through the turbulators is notexcessively great, it is appropriate that the end surfaces 22 of thevanes (as is apparent from FIG. 3) make an angle with a diametric planeto the inner core 8 such that, thereby, the leading and trailingsurfaces of the turbulators 10 in the flow direction will beapproximately conical. Furthermore, the end surfaces 22 should berounded or spiculated.

According to the invention, the through flow channels located betweenthe vanes 21 should have larger cross-sectional areas than is the casefor the material cross-section in the vanes. Furthermore, the vanes aresuitably slightly broader at their root portions than at their outerportions. The total of the through flow areas in each turbulator shouldapproximately correspond to the through flow area in the chargingchannel 9, which has been realised in that the channels in theturbulators are of greater radial extent than is the case for theannular charging channel 9.

It will also be apparent from FIG. 3 that the turbulators 10 disposed ingroups of two have therebetween a short gap so that there is formed anannular space between proximally located end surfaces 22. Furthermore,the turbulence members or vanes 21 are offset in the circumferentialdirection on proximally located turbulators, whereby, for example, theend surfaces 22 will be located in register with the through flowchannels 23 on the adjacent turbulator. Naturally, other mutual offsetrelationships may also be employed, even though the above-mentionedconfiguration has proved to be the most efficient for its purpose.

Since the sole purpose of the through flow channels 23 is to createturbulence, and a possible helical flow pattern in the charging channel9, the through flow channels 23--and consequently also the vanes21--need not be of excessively great axial length. Practical experimentshave shown that a length along the longitudinal direction of thecharging channel 9 of roughly the same order of magnitude as the innerdiameter of the outer body 7 is suitable. Furthermore, experiments havedemonstrated that an angle of pitch, i.e. the angle between thelongitudinal direction of the vane 21 and a plane at right angles to thelongitudinal direction of the charging channel 9 of approximately 45°for the vanes 21 is suitable, even though other angles ofpitch--appropriately in the range of between 30 ° and 60°--may also beemployed.

If different angles of pitch for the vanes 21 are relevant, theselection of angles of pitch should suitably be placed in relationshipto the axial flow rate in the annular charging channel such that a highaxial flow rate requires a greater angle of pitch for the vanes, andvice versa.

While not being apparent from the Drawings, the pitch for all of theturbulators faces in the same direction, so that, thereby, the flowthrough the annular charging channel will follow a helical course withrotation in the same direction throughout the entire length of thechannel 9. However, it is naturally conceivable to switch the directionof pitch of the turbulators so that the rotation will becounter-directed along different portions of the annular chargingchannel 9.

In order to adapt the turbulators to the flow pattern which prevails ateach respective turbulator, it is also possible to provide a large pitchfor those turbulators which lie most proximal the inlet device (wherethe flow is substantially axial) and then gradually reduce the pitch thefurther away from the inlet device the turbulator in question is located(where the flow already rotates). Hereby, the pitch which the rotatingflow experiences in the channel 9 could become approximately constantfor all turbulators.

The present invention should not be considered as restricted to thatdescribed above and shown on the Drawings, many modifications beingconceivable without departing from the spirit and scope of the appendedclaims.

What is claimed is:
 1. An apparatus in a powder sprayer comprising anannular friction charging channel (9) defined by an inner, longitudinalbody (8) and an outer, tubular body (7) surrounding the inner body,there being disposed, in the flow path of the powder through thesprayer, at least one turbulator (10) with turbulence members (21) whichare obliquely inclined or helically configurated in relation to thelongitudinal direction of the sprayer said turbulence members beingshaped as substantially radially extending vanes spaced along thecircumference of the annular channel, characterised in that at least twoturbulators (10) are disposed in the annular channel (9); and that theannular channel (9) has a bigger radial extent immediately upstream anddownstream of a turbulator (10) and within the area of the turbulatorthan is the case at remaining portions of the annular channel.
 2. Theapparatus as claimed in claim 1, characterised in that the size of thethrough flow area of the annular channel (9) approximately coincideswith the size of the through flow area of flow channels (23) through theturbulators (10).
 3. The apparatus as claimed in claim 1 or 2,characterised in that, the turbulence members (21) of adjacentturbulators (10) are distributed about the longitudinal body (8) suchthat the turbulence members (21) of a downstream turbulator are alignedwith the flow channels (23) between adjacent turbulence members (21) ofan upstream turbulator.
 4. The apparatus as claimed in claim 1 or 2,characterised in that the turbulators (10) are disposed in groups of twoor more in mutual sequence after one another.
 5. The apparatus asclaimed in claim 1 or 2, characterised in that, the radially outermostportions of the turbulence members (21) abutt the inner surface ofturbular body (7) to thereby center the inner body (8).
 6. The apparatusas claimed in claim 2, characterised in that the cross-sectional area ofone vane (21) is less than the through flow area in one channel (23). 7.The apparatus as claimed in claim 1 or 2, characterised in that theturbulence members (21) or the vanes, respectively, have an angle ofpitch in relation to a plane at right angles to the longitudinaldirection of the charging channel (9) in the range of between 30° and60°.
 8. The apparatus as claimed in claim 1 or 2, characterised in thatthe axial length of each turbulator (10) approximately corresponds tothe inner diameter of the tubular body (7).